Vania



Filed Aug. 2, 1924 Patented Get. i6, 192%.

narraa GEORGE DONALD VIELTY, 01E CLEVELAND,

on AMERICA, or rrrrsnunsn, Paints VANIA.

Git-"TO, ASSIGNOR- TO ALUMINUM! COMPANY YLVAE ll. CCEPOEATION OF PENNSYL- PEUCES$ OF MAKING Z-ZGLLQV] Application filed August 2,

This invention relates to annular metallic articles, particularly expanded or contracted tubular articles and to a method of making such articles.

It further relates to a method of making tubular articles which are to be split in a longitudinal direction by which the tendency of the article to expand or contract when split aswell as the amount of such expansion or contraction, may. be determined and controlled. I

it also relates to a method of making an annular metallic article adapted to expand or contract radially a predetermined and controllable amount when split lengthwise.

It further relates to tubular ar icle characterized by possessing increased resistance to contraction or collapse when split length wise for a part or all of its length.

My invention is based on the discovery that internal strains of compression or tension may be put into a tubular, metallic article by cooling the outside and inside at different rates and that these strains may be predetermined and controlled so that when the wall of the article is split in a longitudinal direction throughout all or part of its length, it ill tend to expandor to contract according to the nature and the magnitude of thestrains which hav'e been set up.

The preferred method of practicing my invention consists briefly of suitably quenching or cooling the exterior or interior of a suitably heated annular or tubular article at an unequal rate to set up internal strains of tension or compression of the desired magnitude, then splitting the article in a lcngthwise direction, the determination of the surface to be cooled the more rapidly depending on whether expansion or contraction of the article, after splitting, is desired.

In the drawings accompanying this specification and forming a part thereof, in which i haveillustrated two different structures embodying my invention. r

Figure 1 is a perspective view of a tubular article upon which my invention may be practiced. V

Figureil is across sectional view taken on line 22 of Fig. 1 showing a tube subjected to my improved process before and after'being split lengthwise. V

FigureB is a view corresponding to Fig. 2

1924. Serial No. 7229,6835

but showing, before and after split ing. a tube subjected to the variation of my process to cause contraction after splitting.

Figure 4 is a cross sectional view of a conventional form of piston provided with circumferentially and longitudinally extending intersecting slits in the skirt, and

n igurc 5 is a cross sectional view taken substantially on line 5-5 of Fig. 4 showing before and after splitting the piston of Fig. 4

'iich had been subjected to my method to produce expansion or splitting.

Annular metallic articles when suddenly cooled or quenched from fairly high tempera tures have internal strains set up in them which strains depend on the nature and extent of the chilling. If the rate of chilling is unequal on the inner and outer surfaces of the article. the strains tend to distort the article when it is split lengthwise, the distortion occurringin a direction dependent upon the pl of application of the greater chilling action and to an amount dependent upon the extent of the chilling action. For example, an annular or tubular article may be quenched in a manner to cause the article, when split lengthwise, to contract or to expand, or to remain unchanged; and by suitably regulating the extent of the quenching of the article, the amount of this contraction or expansion can be predetermined and repeated with a high degree of uniformity.

My invention is broadly applicable to metallic articles which are, in general, annular, tubular or continuous hollow shells and it is not restricted to such articles when composed of any particular metal or alloy. It may be practiced on cast articles or those which have been previously worked. For example, my method of treatment may be practiced on drawn or extruded tubes of steel, aluminum alloys or other metals, 'as well as on pistons for internal combustion engines, composed of cast iron or aluminum base alloys. It will, o't course he understood that articles of various shapes, sizes and compositions will require different quenching temperatures and that the determination of such temperatures will depend upon the composition and nature of the article in question, and the amount of distortion desired in the treated article. In general. the strains are proportional to the severity of the chilling consequently substantially the same amount of distortion may be obtained by quenching from different tcmperatures provided the quenching agent or the temperature thereof is suitably varied to cause substantially the same rate of cooling. For example, an article may be cooled from a high temperature by a relatively slow cooling medium and a similar article may be given substantially the same properties by cooling from a lower temperature with a more rapid cooling agent. The s iecilic examples given hereinafter will serve, however, to guide those skilled in the art in practicing my invention on articles of various sizes, sha es, natures and compositions.

In the drawings-Figs. 1, 2 and 3 are various views of a drawn steel tube 1.. This tube,

-when heated to about 1500 F. and then cooled by quenching the inner surface, will possess the property of expanding from the dotted line position to the full line position of Fig. 2 when it is split lengthwise as by slit 2. After being split, the tube 1 may still retain the property of: further expansion when it is heated sufiicicntly or when it is struck or ja red so as to relieve the internal strains. If the outer surface instead of the inner surface is quenched from a te-n'n ierature of about 1500, the tube will then possess the property of contracting upon being slit lengthwise, as shown in Fig. 3 where the dotted lines indicate the position of the tube before splitting and the full lines the position after splitting. It will be understood that these indicated changes are greatly exaggerated in the figures, the actual change being only a few thousandths of an inch- Vith a three inch tube having wa ls thick the expansion or contraction may amount to between about .001 and .003 when quenched from 1500 F. in water at a temperature of about 50 F. In general, the more severe the quenching the greater will. be the tendency of the article to expand or contract. that is, distort and when the quenching of a number of similar articles is of substantially the same severity, the articles will possess the tendency of distortion to substantially the same extent.

My invention is of particular utility when applied to an internal combustion engine piston of the so-called split skirt type, where in one or more of the bearing faces of the skirt are provided with intersecting circumferential and longitudinal slits. In pistons of this type treated in accordance with this invention there is a tendency toward cxpansion of the free ends of the sections in the skirt along the lengthwise slit, as contrasted with a corresponding tendency to contraction, or to contraction of one section and expansion of another section in permanent mold cast pistons not so treated. Equal expansion of these split sections is desired because it tends to maintain undiminished the original bearing area of the skirt and to make possible close fitting of the piston to its cylinder and maintenance of substantially the original clearance during the major part of or all the life of a piston.

In applying my invention to tubular articles having a closed end, as illustrated by an internal combustion engine piston, distortion may be produced in the same manner as in the tube shown in Figs. 1 to 3, inclusive, except that in the piston the actual distortion may be confined to a portion only of the skirt, whereas in Figs. 1, 2 and 3 it has been illustrated as being more or less uniformly distributed throughout the entire circumferential length of the article.

Figs. 4 and 5 show a conventional form of piston 3 having a circumferentially extending slit 4 and a. longitudinally extending slit 5 intersecting therewith, these slits being formed in what is known as one of the two bearing faces 6 of the piston. The dotted and full lines in Fig. 5 indicate respectively, the positions before and after slitting of a. piston skirt subjected to my method to cause expansion after splitting, the amount of change being greatly exagge'ated. The piston 3, when cast in a permanent mold of an aluminui-n base alloy containing say between about 4% and about 16% of copper or copper and other heat responsive hardening metals, such as silicon and magnesium, with or without nickel, manganese, chromium, and with or without other metals, may be subjected to my improved process in one or more difierent ways.

It may be suitably quenched or may be cooled more rapidly on the inner than on the outer surface, as it comes from the mold in a highly heated condition, and then split; or it may be cooled in the open air to room temperature after being removed from the mold then reheated at a high temperature for the desired length of time, quenched more rapidly' on the inner than on the outer surface and then split but preferably it should be cooled in the openv air to room temperature afterleaving the mold, then heated to a high temperature for the desired length of time, quenched more rapidly on the inner than on the outer surface, then aged ata low temperature compared with the high temperature just mentioned, in order to improve such properties as hardness and elastice limit, then machined and split just before putting into the motor. The unequal cooling or quenching step of my method may be accomplished by bringing water, oil or other cooling fluid into the interior thereof, after which the skirt may be split substantially, as shown in 7 Figs. 4. and 5, with the result that the portions of the skirt adjacent to the slits 4 and 5 Will tend to assume substantially the full line positions shown in Fig. 5.

When a diametrical expansion of from about .001" or .005 is desired in the skirt of a piston about 3inches in diameter and composed of an aluminum base alloy of the foregoing composition, 1 may quench the in terior of the piston from temperatures of 7 00 F. to 950 F. but to produce the same re sult atthe lower temperature the temperature ofthe quenching medium should be correspondingly lower so as to produce the same severity of chilling.

The preferred temperature is 950 F. with such compositions because at such temperature the article possesses the maximum potentiality for hardening.

The temperature of the quenching medium such as water, to be used with a. piston of the foregoing composition and at 950 F. is

about 50 F. when an expansion of from- .001 to about .005 i desired. Although water has been mentioned hereinabove as a suitable quenching medium, it will be un derstood by those skilled in the art that oil may be similarly employed, but when the same severity of chill is desired the temperature of the oil should be considerably lower than that of the water For example, when the cast iron tube mentioned hereinabove is to be quenched from a temperature of about 1500 in oil instead of water, the oil should be maintained at somewhere about 30 F. in order to obtain the same severity of chill as when the water is employed at a temperature of about 50 F.

Pistons of such composition when quenched in accordance with my invention not only expand when split but possess the property of tending to expand still more when struck, jarred or subjected to the ordinary usage of pistons in internal combustion engines. They are thus capable of resisting any tendency of the skirt portions along the slits to spring inwardly when the skirt is split or to be pressed inwardly by the cylinder walls.

lVhen t-heinner and outer surfaces of an article heated in accordance with my invention are quickly cooled or quenched at substantially the same rate, the internal strains are either absent or tend to balance each other and the article tends neither to expand nor contract when split lengthwise thereafter.

I believe the strains set up by my treatment to be strains of compression and tension; and that in general when one surface of an annular article is'quenehed by my method that surface has compression strains set up in it while the opposite surface has tension strains set up in it. This belief and theory may not be the real explanation, however, and consequently I do not wish to be bound thereby. The scope of my invention is set forth in what is claimed.

'lVhat is claimed is:

1. The method of makin an annular metallic article which comprises subjecting the inner and outer surfaces of a circumferentlally continuous annular metallic article in a mechanically unrestrained condition respectively toheat treatments differing in degree thereby setting up internal compression strains near one surface in excessof similar strains near the other surface, and then slitting the article in a lengthwise direction for at least a part of its length.

2. The method of making an annular metallic article having a longitudinally exte ded slit which comprises heating circumferentially continuous annular a circumferentially continuous annular metallic article ina mechanically unrest-rained condition to such a tempcrature that internal strains will set up therein when the surfaces of the article suddenly and unequally cooled or quenched, quenching the inner surface of the articlein a manner to set up greater strains adjacent thereto than adjacent to the outer surface, and splitting the article lengthwise for a part or all of its length.

l. The method of making an annular, metallic article which comprises subjecting the inner and outer surfaces of a circumferentially continuous annular metallic article in a mechanically unrestrained condition respectively to heat treatments differing in degree thereby setting u 3 internal unbalanced strains in the said article, and then splitting the article in a lengthwise direction for at least a part of its length.

5. The method of making a contracted annular metallic article which comprises heating a circumferentially continuous annular metallic article in a. mechanically unrestrained condition to such a temperature that internal strains will be set up therein when the surfaces of the article are suddenly and unequally cooled or quenched from the said temperature, quenching the outer surface of the said article from the said temperature in a manner to set up the internal strains of greatest magnitude adjacent to the inner surface thereof, and splitting the article in a lengthwise direction for a part or all of its length.

6. The method of making an expanded tubular article composed of an aluminum base alloy, which comprises heating an unsplit tubular article composed of such material to a temperature of between about 700 F.

to 050 F., quenching the inner surface thereof in a manner to set up the internal strains of greatest magnitude adjacent to. the inner surface, and then splitting the said article lengthwise for at least a part of its length.

' The method of making a contractul tubular article composed of an aluminum base alloy, which comprises heating an unsplit tubular article composed of such material to a temperature of about 050 F., quenching the outer surface thereof in a manner to set up the internal strains of greatest magnitude adjacent to the outer su face and then splitting the said article lengthwise for at least a part of its length.

8. The method of providing an internal combustion engine piston with an expanded skirt which comprises acting upon the circumferentially continuous skirt of a piston in a manner to set up interior compression strains in the inner surface of the skirt portion of the piston, and then forming intersecting slits in the said skirt.

9. The method of providing an internal combustion engine piston with an expanded skirt which comprises heating a piston having a circumferentially continuous skirt portion to such a temperature that interior compression strains will be set up near the surface of the skirt when the surface thereof is suddenly cooled or quenched, quenching the inner surface of the said skirt, and forming intersecting slits in the skirt portion of the said piston.

10. The method of providing an interior combustion engine piston with an expanded skirt and composed of an aluminum base alloy which comprises heating a piston having a circumferentially continuous skirt and composed of an aluminum base alloy to a temperature from about 700 F. to about 950 F, quenching the interior surface of the said skirt and finally forming intersecting slits in the said skirt.

11. The method of providing an internal con'ibustion engine piston composed of an aluminum base alloy with an expanded skirt which comprises heating an aluminum base alloy piston casting having a circumferentialiy continuous skirt to a temperature of between about 700 F. to about 950 F., cooling the heated casting in a manner to set up internal compression strains near the inner su face thereof, and forming intersecting slits in the skirt of the cooled casting.

12. The method of providing an aluminum base alloy piston with a skirt of the split type which comprises heating a piston having a circumferentially continuous skirt to a temperature of approximately 950 F., cooling the piston by quenching the inner surface of the skirt in oil or water and forming intersecting slits in the skirt of the thus cooled GEORGE DONALD WELTY. 

